Products that have decorative patterns formed on the surface of the products by abrasion (typically sandblasting) or etching are becoming increasingly more popular. A wide variety of techniques have been developed to effectively produce masks to facilitate accurate production of such objects, such as shown in U.S. Pat. Nos. 5,370,762, 4,764,449, and 5,427,890 (the disclosures of which are hereby incorporated by reference herein), and various automated equipment has been developed to facilitate processing during production of such masks (such as shown in U.S. Pat. No. 5,366,584). The basic processes utilize a photoresist laminate which may have a variety of constructions, but includes a substrate and an outer layer of photoresist material (radiation sensitive material which is soluble or dispersible in water but will harden upon sufficient exposure to radiation so as to become substantially insoluble or non-dispersible) facing outwardly from the substrate. The photoresist laminate is typically provided in roll form where the radiation sensitive material of one part of the roll contacts a substrate on another part of the roll; or the laminate may be provided in sheet form with one sheet stacked upon another with the radiation sensitive material of one sheet contacting the substrate of another. Under some circumstances, especially where there is high humidty or products have been maintained in a roll or stacked configuration for a long period of time, a problem of sticking may occur. That is, the photoresist material sticks to the substrate of an engaged part of the roll, or of another sheet. This can be a significant problem since sticking may cause the photoresist material to be removed or separated from the substrate, and make it unusable for its intended purpose.
Another problem can occur when the photoresist is exposed to UV radiation. The pattern that creates the latent image is printed on a paper vellum or plastic film. This pattern is pressed onto the surface of the photoresist during its exposure to radiation. A sticky photoresist material can cause paper vellums to tear or pull off the ink that creates the pattern. The sticking can also cause delamination between the photoresist and the substrate film when the vellum is removed.
In order to overcome this problem, various types of substrates have been attempted to be utilized, with less than optimum success in preventing or minimizing the sticking problem. Also providing a release liner on top of the radiation sensitive material (photoresist material) which is removed prior to use significantly increases the costs of the laminate, makes the laminate bulkier to ship, and introduces another step for the utilization thereof.
According to the present invention a photoresist laminate, a stencil made therefrom and a method of utilization thereof for abrading or etching, are provided which substantially eliminate or minimize the sticking problem in a simple and effective manner, without significantly increasing the cost of the laminate, and without introducing another step for utilization thereof. According to the present invention, during manufacture the radiation sensitive material is provided with a very thin coating which is readily removed during processing, and does not significantly interfere with the radiation sensitivity of the photoresist material, yet it substantially prevents sticking of the photoresist material to a substrate of an adjacent portion of the laminate in a roll, or of another sheet in the stack, or even to other materials that the photoresist material may inadvertently come into contact with.
According to one aspect of the present invention a photoresist laminate is provided comprising the following components: A substrate having first and second faces. A first film layer of radiation sensitive material which is soluble or dispersible in water but will harden upon sufficient exposure to radiation so as to become substantially insoluble of non-dispersible, and operatively disposed on the substrate first face. And a second layer of a material and thickness so that it substantially prevents or minimizes sticking of the first film layer while not significantly interfering with the radiation sensitivity thereof. The second layer is on the opposite side of the first film layer from the substrate.
The photoresist laminate may comprise other layers and constructions. For example, a membrane support layer may be provided between the substrate and the first film layer and engaging both the substrate and the first film layer. Also, or alternatively, the first film layer may comprise two clearly different colored portions, one atop the other, specifically as described in said copending application Ser. No. 09/137,702; and the laminate may consist of the recited elements above.
Typically, the second layer has a maximum thickness of about 0.0005 inches, e.g. about 0.0003 inches, and most desirably between 0.0001-0.0002 inches. While any material suitable for performing the non-stick, yet not interfering with the radiation sensitivity, functions may be provided, one particularly desirable material for forming the second film layer comprises a mixture of polyvinyl alcohol solution and polyvinyl acetate emulsion. The range may be 2-98% by weight of one and 98-2% of the other. If a water soluble formula is desired so as to facilitate wash-away of the second layer during processing, preferably about 80%-98% by weight polyvinyl alcohol solution with the remainder polyvinyl acetate solution (and perhaps some inert materials is provided). If a substantially water insoluble formulation is desired it comprises about 80-98% by weight polyvinyl acetate solution with the remainder polyvinyl alcohol solution (and perhaps inert ingredients).
The second layer may be applied in a conventional coating process (e.g. direct roll coating) after the rest of the laminate has been formed, or may be provided by spraying a fine spray of the second layer material on the first layer, to form a fine film, using conventional aerosol equipment.
A variety of thicknesses and materials may be utilized. For example the first film layer may have a thickness of between about 0.002-0.009 inches may be a conventional photoresist material such as described in said copending application Ser. No. 09/137,702, or a positive or a negative acting film such as described in U.S. Pat. No. 4,764,449, or of any other conventional construction such as shown in U.S. Pat. No. 5,427,890. The substrate typically has a thickness of about 0.002-0.003 inches and may comprise PET film, or Mylar.RTM. polyester film (e.g. type S-200 gauge), or any other conventional substrate. The membrane support layer, when utilized, may have a thickness of between 3-5 microns and also may comprise any suitable conventional material. Other layers are also possible depending upon the particular use or circumstances, again such as described in U.S. Pat. No. 4,764,449.
The laminate may be in a roll form with the second layer contacting the second face of the substrate in a substantially non-stick manner. Alternatively, the laminate may be in sheet form, and stacked with other substantially identical laminates so that the second layer of one sheet engages the second face of the substrate of another sheet.
The laminate as described above preferably is utilized in a method of making a stencil and ultimately an etched or abraded object, such as described in either the inventive or background portions of copending application Ser. No. 09/173,702. For example, by utilizing the laminate as described above a method of making a stencil for abrading or etching using a negative acting or positive acting photoresist laminate as described above, is provided comprising: (a) Exposing the laminate and a pattern to radiation to cause hardening of some portions to define the pattern as a latent image in the photoresist first film layer by providing some portions that are soluble or dispersible in water, and other portions that are substantially insoluble or non-dispersible. (b) Processing the laminate from (a) by spraying water on the laminate to remove the soluble or dispersible portions of the first layer, and at least those portions of the second layer covering the soluble or dispersible portions of the first layer, but not the substantially insoluble or non-dispersible patterns of the first layer to ultimately produce a stencil. And (c) using the stencil from (b) as a mask on the surface of an object to etch or abrade the surface of the object where the photoresist film has been removed to form a surface texture in the object that stimulates the latent image.
Where the first layer comprises first and second clearly different colored portions, one atop of the other, then (b) is practiced to first remove substantially all of the soluble or dispersible portions of the first color, and only then to carefully start to remove the soluble or dispersible portions of the second color. The invention also relates to a stencil produced by practicing (a) and (b) of the method as described above.
It is the primary object of the present invention to provide a photoresist laminate which substantially eliminates or minimizes the sticking problem present in conventional photoresist laminates, in a simple and cost effective manner, which does not require changes in the method of utilization thereof to produce a stencil for masking and ultimately producing an etched or abraded object. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.